very easily done
there is a release from mm re upgrading the specs of the ml with the heavy duty towbar

or i checked with an authorised hayman reece towbar supplier (on recommendation from Jayco Brisbane) who checked the vin number against the towbar fitted and simply applied for a new compliance sticker as everything matched Didnt cost me anything from memory. just a new sticker for the towbar itself ( i had to grind off the old plate )
and a new sticker for the door. There is a national registry? apparently on what vehicles can have re towbar weights
.From memory most of the earlier japanese 4wd eg series 2 pajero later models prados etc are very conservative in their original specs, most can be upgraded by simple application

One interesting thing that I noted from that release was that in the 1350kg to 2500kg range a weight distribution hitch was specified to be used for specifically the NM with trailer brakes.
The other models were not singled out.
Might this possibly be due to changes in suspension?